TRAVELS OF WATERFOWL 

 coated hunter crawling in front of autumn cattails), and if the object moves 

 slowly, awareness of motion is difficult But where the background is sta- 

 tionary, the color contrast sharp between background and object, and the 

 movement rapid, awareness is keen. We must judge that ducks are more 

 successful than men in detecting motion under adverse conditions of speed 

 and background. Their field of movement perception is probably greater 

 than that of men not only because of the position and structure of the eye, 

 but because of their different response to the environment. Men are highly 

 sensitive to movement on a horizontal plane, since they meet their world 

 largely between their feet and the horizon. Ducks, on the other hand, meet 

 the world from above when flying ; and they must be ever aware of their aerial 

 environment when on the ground. 



The visual world of the waterfowl, then, while probably having the same 

 colors as that of man, is much wider. It is viewed monocularly, and more 

 of its detail is perceived sharply at a glance. Perception of movement is 

 keener than in man, the power to resolve detail is greater, and the avian eye 

 accommodates itself to changes in the position of objects more quickly. It 

 is impossible, with our binocular vision and narrow visual field, to imagine 

 how the world appears to a duck, but it is easy to understand how percep- 

 tion is highly efficient for spatial orientation. 



At this point we must acknowledge that visual perception concerns more 

 than the eye, both in birds and men. The eye is simply the window of the 

 brain. The eyes of a man (and of a bird) receive stimuli, such as rays of 

 light, from the outer world, "and these produce electric changes which are 

 propagated over his nerves to his brain. Here they produce further changes, 

 as the result of which — after a series of processes we do not in the least 

 understand -his mind acquires perceptions, to use Hume's terminology, of 

 the outer world" (Jeans, 1943:6). Bird and man respond not directly to 

 their environment, but only to the image that reaches the brain. Seeing is 

 merely the physical reception of an image; the delicate organ of sight, in 

 effect, is the camera. Perception follows only when the brain has "examined" 

 the image. Thus the visual world depends not only on the nature of the 

 eye, but on that of the brain as well, and each animal lives in its own per- 

 ceptual world which in some way is distinct from that of any other in- 

 dividual. 



We who live outside the worlds of birds study avian perception through 

 their response to their environment. We know they are aware of something 

 only when they show behavior. As we watch the flight of Mallards out to 



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